High variable power zoom lens

ABSTRACT

A variable power zoom lens of four groups of lens pieces respectively exerting positive, negative, positive, and positive refractivities varies the power from the wide-angle end to the telephoto end as a result of the 1st and 2nd lens groups being separated more, the 2nd and 3rd lens groups, and the 3rd and 4th lens groups, coming closer to each other. The 3rd lens group has a leading set of lens pieces closer to the object side having a positive refractivity as a whole and the trailing set of lens pieces have negative refractivity as a whole, and the trailing set alone are moved to be orthogonal to the optical axis to compensate for defocus in the imaging plane. The 2nd lens group is displaced closer to objects for focusing.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a divisional application of U.S.patent application Ser. No. 12/458,314, filed Jul. 8, 2009 now U.S. Pat.No. 8,238,038, which is based on, and claims priority to, JapanesePatent Application No. JP 2008-206018, filed Aug. 8, 2008, JapanesePatent Application No. JP 2008-206019, filed Aug. 8, 2008, and JapanesePatent Application No. JP 2008-206020, filed Aug. 8, 2008, all of whichare incorporated herein in their entireties by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high variable power zoom lenssuitable for a single-lens reflex camera, and more particularly, itrelates to a compact and lightweight, high variable power zoom lens thatis capable of having a sufficient back focal length, suitable for asingle-lens reflex camera, and advantageous in incorporating opticalstabilizer or anti-vibration mechanism, and that is 75 degrees or evenwider in field angle at the wide-angle end, approximately 3 to 4 inF-number at the wide-angle end and approximately 6 to 7 at the telephotoend, and about 15× in variable power ratio.

2. Description of Related Art Including Information Disclosed Under 37CFR §§1.97 and 1.98

The recent drastic advancement in technologies of optical designs andmanufacturing optics has enabled zoom lenses to be downsized more andenhanced in variable power. For instance, one type of the zoom lenses inthe state of the arts have a variable power enhanced design and enableto incorporate an optical stabilizer or anti-vibration feature, whichtypically comprise four groups of lens pieces, namely, the 1st lensgroup of positive refractivity, the 2nd lens group of negativerefractivity, the 3rd lens group of positive refractivity, and the 4thlens group of positive refractivity arranged in this order on the closerto objects first basis where the power is varied from the wide-angle endto the telephoto end as a result of the 1st and 2nd lens groups beingseparated more, the 2nd and 3rd lens groups coming closer to each other,and the 3rd and 4th lens groups being varied in a distance therebetween.The 3rd lens group has a leading set of the lens pieces closer to theobject side having a positive refractivity as a whole and a trailing setof the lens pieces having a negative refractivity as a whole, and thetrailing set alone is moved in position approximately orthogonal to theoptical axis so as to compensate for defocus in the imaging plane causedby a tremor of the user's hand(s), which can be corrected by theanti-vibration feature of which requirements are to satisfy thefollowing formula:3.5<f1/fw<8.0where fw is a focal length of the zoom lens at the wide-angle end, andf1 is the focal length of the 1st lens group (see Patent Document 1listed below).

Another type of the high variable power zoom lenses are compatible withan APS-C dimensioned image sensor and are dedicated to digital cameras,which also have four groups of lens pieces, namely, the 1st lens groupof positive refractivity, the 2nd lens group of negative refractivity,the 3rd lens group of positive refractivity, and the 4th lens group ofpositive refractivity arranged in this order on the closer to objectsfirst basis where the power is varied from the wide-angle end to thetelephoto end as a result of the 1st and 2nd lens groups being separatedto elongate an aerial distance therebetween, and the 2nd and 3rd lensgroups coming closer to each other while simultaneously the 1st, 3rd,and 4th lens groups are moved all together closer to objects. The 2ndlens group are displaced for the focusing of which requirements are tosatisfy the following formulae:0.40<fW/fbW<0.55  (1)0.43<β34W/β34T<0.47  (2)40<r5/d5W<100  (3)1.1<f3/f4<2.6  (4)where fW is a focal length of the zoom lens at the wide-angle end, fbWis a back focal length at the wide-angle end, β34W is a composite powerof the 3rd and 4th lens groups at the wide-angle end, β34T is thecomposite power of the 3rd and 4th lens groups at the telephoto end, r5is a radius of curvature of the surface designated by r5, d5W is adistance between the 1st and 2nd lens groups at the wide-angle end, f3is the focal length of the 3rd lens group, and f4 is the focal length ofthe 4th lens group. This type of the zoom lenses are, regardless oftheir original design concept especially suitable for the APS-C size,able to ensure the same back focusing as those for image dimensions for3.5 mm film (see Patent Document 2).

LIST OF PATENT DOCUMENTATIONS

Patent Document 1

Japanese Patent Unexamined Publication No. 2006-106191

Patent Document 2

Japanese Patent Unexamined Publication No. 2005-331697

As the consumer demands in the camera market have been trending from theconventional silver film cameras to digital single-lens reflex cameras,contaminants likely attached to optical imaging components such ascharge-coupled devices (CCDs) and the like have become a matter ofconcern because of their adverse effects upon the resultant images. Dueto the contaminants onto the CCDs, component lenses must be oftenreplaced, and one of the goals of the newly developed high variablepower zoom lenses is to avoid such frequent replacement. Among thesignificantly advanced group of the improved zoom lenses, none hasattained the variable power higher than 15× while some of the remainingless aggressive groups cover as wide as about 75 degrees in field angleat the wide-angle end and are no more than 3 to 4 in F-number at thewide-angle end.

In general, as the variable power is raised, the lens groups areaccordingly displaced more, associated with the increased variations inaberration, which results in compensation for the aberration being moredifficult throughout the focal range. To overcome this, the lens groupsmust have their respective refractivities diminished to correct theaberration, or some of the lens pieces should be shaped to have anaspherical surface(s) for the same purpose. Reducing the refractivity insuch manners, however, resultantly necessitates the lens groups to bedisplaced more for varying the power as much, and this leads to a morecomplicated cam barrel design as well as an increase in diameter of thezoom lens.

In the zoom lens as described in Patent Document 1, the component lenspiece(s) has an aspherical surface(s), and there are three of the lenspieces in the leading set so as not to increase the number of the lenspieces for correcting the aberration. In the event of the power raisedhigher than 13×, the zoom lens is not able to sufficiently compensatefor spherical aberration that would be caused in the 1st and/or 2nd lensgroups at the telephoto end. In addition, another problem of an increasein the diameter of a filter arises.

The zoom lens disclosed in Patent Document 2 has the variable power ofapproximately 7×, and hence, even if the 3rd lens group has itsrefractivity diminished, it is avoidable that, as a result of varyingthe power of the zoom lens, the refractivity would never be reduced somuch as −1× at which this lens group makes the comprehensive powerinvariable. Raising the variable power of the zoom lens up to 13×results adversely in the zoom lens being in focus at the varied focallength to cause the 3rd lens group to be diminished in power as low as−1× in some case. Additionally, the 3rd lens group becomes moreaberration sensitive, and coping with this kind of troubles brings aboutdisincentive and degrades their productivity.

The present invention is made to overcome the aforementioned problemswith the prior art high power zoom lenses, and accordingly, it is anobject of the present invention, especially of first two aspects of theinvention described later, to provide a high power zoom lens of multigroups of lens pieces that is in focus at the varied focal length neverto cause the 3rd lens group to be diminished in power as low as −1×.

It is another object of the present invention, especially of the firsttwo aspects of the invention described later, to provide a high powerzoom lens of multi groups of lens pieces where the 3rd lens group has areduced sensitivity to aberration, which brings about incentive toenhance their productivity.

It is still another object of the present invention, especially of thefirst two aspects of the invention described later, to provide a highpower zoom lens of which filter is effectively downsized in diameter.

It is yet another object of the present invention, especially of a thirdaspect of the invention described later, to provide a high power zoomlens that facilitates incorporation of an aperture stop controllingmechanism and an optical stabilizer or anti-vibration mechanism byelongating a distance from an aperture stop to ananti-vibration/compensation lens component and a distance from thelatter to an image plane, and that is capable of enhancing the variablepower up to as high as 18-270 mm in focal length.

It is further another object of the present invention, especially of thethird aspect of the invention described later, to provide a high powerzoom lens that has optics of a relatively small longitudinal dimensionand has a filter of a reduced diameter.

BRIEF SUMMARY OF THE INVENTION

In a first aspect of the present invention, there is provided a highvariable power zoom lens of four groups of lens pieces, namely, the 1stlens group of positive refractivity, the 2nd lens group of negativerefractivity, the 3rd lens group of positive refractivity, and the 4thlens group of positive refractivity arranged in this order on the closerto objects first basis, where the power is varied from the wide-angleend to the telephoto end as a result of the 1st and 2nd lens groupsbeing separated more, the 2nd and 3rd lens groups coming closer to eachother, and the 3rd and 4th lens groups also coming closer to each other,and

the 2nd lens group are displaced closer to objects for the focusing ofwhich requirements are to satisfy the following formulae:0.35<f1/ft<0.45  (5)0.04<|f1|/ft<0.065  (6)0.15<f3/ft<0.25  (7)where f1 is a focal length of the 1st lens group, f2 is the focal lengthof the 2nd lens group, f3 is the focal length of the 3rd lens group, andft is the focal length of the entire optics of the zoom lens at thetelephoto end, as a whole.

The first aspect of the invention will be detailed below:

The 3rd lens group has a leading set of lens pieces closer to the objectside having a positive refractivity as a whole and a trailing set oflens pieces having a negative refractivity as a whole, and the trailingset alone is moved to be orthogonal to the optical axis so as tocompensate for defocus in the imaging plane caused by a tremor of theuser's hand(s).

The leading set of the 3rd lens group has three or more positive lenspieces at least one of which is a composite lens joined with a negativelens piece, and another stand-alone negative lens piece(s).

The leading set of the 3rd lens group has at least a single positivelens piece that is 80 or even higher in Abbe number.

The trailing set of the 3rd lens group includes a composite lenscomprising an anterior negative lens piece and a posterior positive lenspiece joined to the same in which the negative lens piece having itsopposite major surfaces as concaved, the composite lens comprising anaspherical surface and the positive lens piece has its surface closer toobjects as convexed.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 80 or even higher in Abbe number.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 1.55 or even higher in refractive index.

Formulae in the First Aspect of the Invention

The formula (5) defines a rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 1st lens group. When therate exceeds the lower limit as defined in the formula (5), the focallength of the 1st lens group becomes shorter, and this is advantageousin downsizing the extension of the zoom lens, as a whole, while it ishard to compensate for spherical aberration and comatic aberration atthe telephoto end. When the rate exceeds the upper limit as defined inthe formula (5), the focal length of the 1st lens group becomes longer,and this means the lens groups are to be displaced more to ensure thefocal length of the zoom lens at the telephoto end, which necessitates amore complicated cam design to unavoidably cause the zoom lens to begreater in radial dimensions. Since the zoom lens at the telephoto endhas the 1st lens group disposed farther apart from the aperture stop,light beams incident upon the 1st lens group pass its periphery, andtherefore, it is hard to compensate for the comatic aberration.

The formula (6) defines the rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 2nd lens group. When therate exceeds the lower limit as defined in the formula (6), the focallength of the 2nd lens group becomes shorter, and this is advantageousin ensuring the same back focusing as that of 35-mm film cameras whileit is hard to compensate for various types of aberration, especially,for field curvature. When the rate exceeds the upper limit as defined inthe formula (6), the focal length of the 2nd lens group becomes longer,and this means the 2nd lens group are to be displaced more to vary thepower, which is disadvantageous in downsizing the entire lens optics.For the purpose of moving the 2nd lens group forward or toward objectsfor the focusing, the 1st and 2nd lens groups must be separated more,allowing for the increased displacement of the 2nd lens group, whichconsequently brings about an increase in the diameter of the filter andthe entire extension of the zoom lens.

The formula (7) defines the rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 3rd lens group. When therate exceeds the lower limit as defined in the formula (7), the focallength of the 3rd lens group becomes shorter, which is advantageous indownsizing the entire lens optics. In this case, however, theperformance is significantly degraded because it is hard to compensatefor spherical aberration, and the 3rd lens group should become moresensitive to the manufacturing tolerances. When the rate exceeds to theupper limit as defined in the formula (7), the focal length of the 3rdlens group becomes longer, and this means the 3rd lens group are to bedisplaced more to vary the power, which is disadvantageous in downsizingthe entire lens optics. Light flux directed from the 3rd lens grouptoward the 4th lens group is almost afocal, and the zoom lens at thewide-angle end has the 3rd lens group diminished in magnification forthe imaging, which brings about an insufficient amount of light aroundthe image plane of the zoom lens at the wide-angle end.

The refractivity of the 3rd lens group, although appropriatelydetermined from the formula (7), yet performs unsatisfactorily to fullycompensate for the spherical aberration caused in the 1st and 2nd lensgroups in an attempt to implement the zoom lens of the variable powermore than 15×. To cope with this, the improved version of the zoom lenstakes an approach to do the compensation with a configuration using fiveof the lens pieces, namely, negative and positive lens pieces jointedtogether, a positive meniscus lens having its posterior surface greaterin radius of curvature, another stand-alone positive lens piece, and asucceeding negative lens piece. If it is desired to further enhance thevariable power, additional positive lens piece(s) may be used.

In addition, to compensate for chromatic aberration that is oftenconspicuous at the telephoto end, it is desirable that at least one ofthe positive lens pieces is 80 or even higher in Abbe number.

Moreover, when the variable power is as high as 15×, the chromaticaberration caused in the 1st lens group is significant at the telephotoend. Especially, to compensate for chromatic aberration ofmagnification, the positive lens piece(s) in the 1st lens groupdesirably has a relatively large Abbe number. Combining two of thepositive lens pieces respectively made of glass having the Abbe numberof 80 or above permits the chromatic aberration of magnification to besufficiently corrected. In general, however, the glass of which Abbenumber is 80 or above has a refractive index smaller than 1.5, and theresultant lens piece has a small radius of curvature. To overcome this,the lens piece must be thicker at its center, and this leads to thegreater diameter of the filter and the increased diameter of the lenspiece. In this improved version of the zoom lens, the lens piece of 80or above in Abbe number is allocated to the second foremost position asa component lens in the 1st lens group while another lens piece of 55 orabove in Abbe number and 1.55 or higher in refractive index is allocatedto the third foremost position. In this way, raising the refractiveindex, as a whole, enables to prevent an increase in the diameter of thefilter and the number of the component lens pieces.

In a second aspect of the present invention, there is provided a highvariable power zoom lens of four groups of lens pieces, namely, the 1stlens group of positive refractivity, the 2nd lens group of negativerefractivity, the 3rd lens group of positive refractivity, and the 4thlens group of positive refractivity arranged in this order on the closerto objects first basis, where the power is varied from the wide-angleend to the telephoto end as a result of the 1st and 2nd lens groupsbeing separated more, the 2nd and 3rd lens groups coming closer to eachother, and the 3rd and 4th lens groups also coming closer to each other,and

the 2nd lens group are displaced along the optical axis for the focusingof which requirements are to satisfy the following formulae:0.35<f1/ft<0.45  (5)0.5<|f2|/fw<0.8  (8)0.15<f3/ft<0.25  (7)where f1 is a focal length of the 1st lens group, fw is the focal lengthof the entire optics of the zoom lens at the wide angle end, f2 is thefocal length of the 2nd lens group, f3 is the focal length of the 3rdlens group, and ft is the focal length of the entire optics of the zoomlens at the telephoto end.

The second aspect of the invention will be detailed below:

The 3rd lens group has a leading set of lens pieces closer to the objectside having a positive refractivity as a whole and a trailing set oflens pieces having a negative refractivity as a whole, and the trailingset alone is moved to be orthogonal to the optical axis so as tocompensate for defocus in the imaging plane caused by a tremor of theuser's hand(s).

The leading set of the 3rd lens group has three or more positive lenspieces at least one of which is a composite lens joined with a negativelens piece, and another stand-alone negative lens piece(s).

The leading set of the 3rd lens group has at least a single positivelens piece that is 80 or even higher in Abbe number.

The trailing set of the 3rd lens group includes a composite lenscomprising an anterior negative lens piece and a posterior positive lenspiece joined to the same, the negative lens piece having its oppositemajor surfaces as concaved, the composite lens comprising an asphericalsurface and the positive lens piece has its surface closer to objects asconvexed.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 80 or even higher in Abbe number.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 1.55 or even higher in refractive index.

Formulae in the Second Aspect of the Invention

The formula (5) defines a rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 1st lens group. When therate exceeds the lower limit as defined in the formula (5), the focallength of the 1st lens group becomes shorter, and this is advantageousin downsizing the extension of the zoom lens, as a whole, while it ishard to compensate for spherical aberration and comatic aberration atthe telephoto end. When the rate exceeds the upper limit as defined inthe formula (5), the focal length of the 1st lens group becomes longer,and this means the lens groups are to be displaced more to ensure thefocal length of the zoom lens at the telephoto end, which necessitates amore complicated cam design to unavoidably cause the zoom lens to begreater in radial dimensions. Since the zoom lens at the telephoto endhas the 1st lens group disposed farther apart from the aperture stop,light beams incident upon the 1st lens group pass its periphery, andtherefore, it is hard to compensate for the comatic aberration.

The formula (8) defines the rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 2nd lens group. When therate exceeds the lower limit as defined in the formula (8), the focallength of the 2nd lens group becomes shorter, and this is advantageousin ensuring the same back focusing as that of 35-mm film cameras whileit is hard to compensate for various types of aberration, especially,for field curvature. When the rate exceeds the upper limit as defined inthe formula (8), the focal length of the 2nd lens group becomes longer,and this means the 2nd lens group are to be displaced more to vary thepower, which is disadvantageous in downsizing the entire lens optics.For the purpose of moving the 2nd lens group forward or toward objectsfor the focusing, the 1st and 2nd lens groups must be separated more,allowing for the increased displacement of the 2nd lens group, whichconsequently brings about an increase in the diameter of the filter andthe entire extension of the zoom lens.

The formula (7) defines the rate of the focal length of the zoom lens atthe telephoto end to the focal length of the 3rd lens group. When therate exceeds the lower limit as defined in the formula (7), the focallength of the 3rd lens group becomes shorter, which is advantageous indownsizing the entire lens optics. In this case, however, theperformance is significantly degraded because it is hard to compensatefor spherical aberration, and the 3rd lens group should become moresensitive to the manufacturing tolerances. When the rate exceeds to theupper limit as defined in the formula (7), the focal length of the 3rdlens group becomes longer, and this means the 3rd lens group are to bedisplaced more to vary the power, which is disadvantageous in downsizingthe entire lens optics. Light flux directed from the 3rd lens grouptoward the 4th lens group is almost afocal, and the zoom lens at thewide-angle end has the 3rd lens group diminished in magnification forthe imaging, which brings about an insufficient amount of light aroundthe image plane of the zoom lens at the wide-angle end.

The refractivity of the 3rd lens group, although appropriatelydetermined from the formula (7), yet performs unsatisfactorily to fullycompensate for the spherical aberration caused in the 1st and 2nd lensgroups in an attempt to implement the zoom lens of the variable powermore than 15×. To cope with this, the improved version of the zoom lenstakes an approach to do the compensation with a configuration using fiveof the lens pieces, namely, negative and positive lens pieces jointedtogether, a positive meniscus lens having its posterior surface greaterin radius of curvature, another stand-alone positive lens piece, and asucceeding negative lens piece. If it is desired to further enhance thevariable power, additional positive lens piece(s) may be used.

In addition, to compensate for chromatic aberration that is oftenconspicuous at the telephoto end, it is desirable that at least one ofthe positive lens pieces is 80 or even higher in Abbe number.

Moreover, when the variable power is as high as 15×, the chromaticaberration caused in the 1st lens group is significant at the telephotoend. Especially, to compensate for chromatic aberration ofmagnification, the positive lens piece(s) in the 1st lens groupdesirably has a relatively large Abbe number. Combining two of thepositive lens pieces respectively made of glass having the Abbe numberof 80 or above permits the chromatic aberration of magnification to besufficiently corrected. In general, however, the glass of which Abbenumber is 80 or above has a refractive index smaller than 1.5, and theresultant lens piece has a small radius of curvature. To overcome this,the lens piece must be thicker at its center, and this leads to thegreater diameter of the filter and the increased diameter of the lenspiece. In this improved version of the zoom lens, the lens piece of 80or above in Abbe number is allocated to the second foremost position asa component lens in the 1st lens group while another lens piece of 55 orabove in Abbe number and 1.55 or higher in refractive index is allocatedto the third foremost position. In this way, raising the refractiveindex, as a whole, enables to prevent an increase in the diameter of thefilter and the number of the component lens pieces.

In a third aspect of the present invention, there is provided a highvariable power zoom lens of multi groups of lens pieces, namely, the 1stlens group of positive refractivity, the 2nd lens group of negativerefractivity, the 3rd lens group of positive refractivity, and the 4thlens group of positive refractivity arranged in this order on the closerto objects first basis, where the power is varied from the wide-angleend to the telephoto end as a result of the 1st and 2nd lens groupsbeing separated more, the 2nd and 3rd lens groups coming closer to eachother, and the 3rd and 4th lens groups also coming closer to each other,and

the 3rd lens group has a leading set of lens pieces closer to the objectside having a positive refractivity as a whole and a trailing set oflens pieces having a negative refractivity as a whole, and the trailingset alone is moved in position orthogonal to the optical axis tocompensate for defocus in the imaging plane caused by a tremor of theuser's hand(s) while the 2nd lens group are displaced closer to objectsfor the focusing of which requirements are to satisfy the followingformula:0.14<|f3r/ft|<0.18  (9)where f3r is a focal length of the trailing set of the 3rd lens group,and ft is the focal length of the entire optics of the zoom lens at thetelephoto end.

The third aspect of the invention will be detailed below:

The 3rd lens group has its trailing set alone moved in positionorthogonal to the optical axis so as to compensate for defocus in theimaging plane caused by a tremor of the user's hand(s).

The leading set of the 3rd lens group has three or more positive lenspieces at least one of which is a composite lens joined with a negativelens piece, and another stand-alone negative lens piece(s).

The leading set of the 3rd lens group has at least a single positivelens piece that is 80 or even higher in Abbe number.

The trailing set of the 3rd lens group includes a composite lenscomprising an anterior negative lens piece and a posterior positive lenspiece joined to the same, the negative lens piece having its oppositemajor surfaces as concaved, the composite lens comprising an asphericalsurface and the positive lens piece has its surface closer to objects asconvexed.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 80 or even higher in Abbe number.

The 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 1.55 or even higher in refractive index.

Formulae in the Third Aspect of the Invention

When the value |f3r/ft| exceeds the lower limit as defined in theformula (9), the power of the lens groups dedicated to stabilizingoptics or anti-vibration is enhanced, and these lens groups are nolonger to be displaced so much, which is effective in avoiding anincrease in the diameter of the displaced lens groups although itproduces an adverse effect of inability to compensate for comaticaberration at the telephoto end. In addition, the anti-vibration bringsabout greater variations in distortion aberration at the wide-angle end.The value f3r/ft exceeds the upper limit, the lens groups are to bedisplaced more for stabilizing the optics, and it is unavoidable thatthe displaced lens groups should have an increased diameter.

As mentioned above, the high variable power zoom lens in the firstaspect of the present invention is capable of satisfactorilycompensating for the spherical aberration caused in the 1st and 2nd lensgroups at the telephoto end, and the zoom lens is in focus at the variedfocal length never to cause the 3rd lens group to be diminished in poweras low as −1×.

The high variable power zoom lens in the first aspect of the inventionhas the 3rd lens group reduced in sensitivity to the aberrations, whichbrings about an incentive to enhance their productivity.

The high variable power zoom lens in the first aspect of the presentinvention has a filter of which diameter is effectively downsized.

The high variable power zoom lens in the second aspect of the presentinvention is capable of satisfactorily compensating for the sphericalaberration caused in the 1st and 2nd lens groups at the telephoto end,and the zoom lens is in focus at the varied focal length never to causethe 3rd lens group to be diminished in power as low as −1×.

The high variable power zoom lens in the second aspect of the inventionhas the 3rd lens group reduced in sensitivity to the aberrations, whichbrings about an incentive to enhance their productivity.

The high variable power zoom lens in the second aspect of the presentinvention has a filter of which diameter is effectively downsized.

The high variable power zoom lens in the third aspect of the inventionfacilitates incorporation of an aperture stop controlling mechanism andan optical stabilizer or anti-vibration mechanism by elongating adistance from an aperture stop to an anti-vibration/compensation lenscomponent and a distance from the latter to an image plane, and the zoomlens is capable of enhancing the variable power up to as high as 18-270mm in focal length.

The zoom lens in the third aspect of the invention has a reduced entireextension of the optics, as a whole, and also has a filter of thereduced diameter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view illustrating optics of a preferred embodimentof a high variable power zoom lens at the telephoto end according to thepresent invention.

FIG. 2 illustrates graphs of axial spherical aberration, astigmatism,and aberration of distortion in the exemplary zoom lens at thewide-angle end.

FIG. 3 illustrates graphs of comatic aberration in the exemplary zoomlens at the wide-angle end.

FIG. 4 illustrates graphs of the axial spherical aberration, theastigmatism, and the aberration of distortion in the exemplary zoom lensat its intermediate focal range.

FIG. 5 illustrates graphs of the comatic aberration in the exemplaryzoom lens at the intermediate focal range.

FIG. 6 illustrates graphs of the axial spherical aberration, theastigmatism, and the aberration of distortion in the exemplary zoom lensat the telephoto end.

FIG. 7 illustrates graphs of the comatic aberration in the exemplaryzoom lens at the telephoto end.

FIG. 8 illustrates graphs of the comatic aberration with a varied fieldangle when the 3rd lens group is displaced by +0.07 mm in verticaldirections relative to the optical axis in the exemplary zoom lens atthe wide-angle end.

FIG. 9 illustrates graphs of the comatic aberration with the variedfield angle when the 3rd lens group is displaced by +0.47 mm in verticaldirections relative to the optical axis in the exemplary zoom lens atthe telephoto end.

FIG. 10 illustrates graphs of the comatic aberration with the variedfield angle when the 3rd lens group is displaced by −0.47 mm in verticaldirections relative to the optical axis in the exemplary zoom lens atthe telephoto end.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of a high variable power zoom lens according tothe present invention will now be described.Focal Length f=18.40˜71.10˜264.21 mmFno=3.50˜5.24˜6.322w=76.5˜23.1˜6.3°

NO R D Nd νd 1 94.3524 1.5000 1.84666 23.78 2 66.4807 8.0000 1.4970081.61 3 −1326.8193 0.2000 1.00000 4 72.3127 4.5000 1.61800 63.39 5180.4067 D5 1.00000 6 90.3327 0.2000 1.51460 49.96 7 83.8997 1.20001.80400 46.58 8 14.845 6.4000 1.00000 9 −34.8049 1.0000 1.80400 46.58 1047.2288 0.8000 1.00000 11 34.7194 4.8000 1.84666 23.78 12 −33.65971.2000 1.00000 13 −25.046 1.0000 1.88300 40.78 14 −207.5416 D14 1.0000015 0.0000 1.0000 1.00000 16 37.3663 1.0000 1.84666 23.78 17 26.49464.0000 1.48749 70.21 18 −1075.5953 0.2000 1.00000 19 32.6392 3.29181.48749 70.21 20 −111.6338 0.2000 1.00000 21 25.7859 4.1440 1.4970081.61 22 3099.5581 1.0000 1.83400 37.17 23 76.3793 2.7717 1.00000 24−56.3646 0.2000 1.53610 41.20 25 −56.3646 1.0000 1.77250 49.60 2633.9463 2.2000 1.80810 22.80 27 68.76 D27 1.00000 28 46.2651 0.20001.51460 49.96 29 46.2651 4.0000 1.48749 70.21 30 −30.1602 0.2000 1.0000031 146.4471 4.0000 1.48749 70.21 32 −31.1609 1.0000 1.80400 46.58 3350.4511 1.2000 1.00000 34 92.7722 4.0000 1.48749 70.21 35 −43.2518 BF

Distances D5, D14, D27, and variations in the back focal length BFduring the zooming are given as follows:

Focal Length f 18.400 71.099 264.210 D5 2.058 39.047 68.462 D14 30.53911.868 1.055 D27 7.717 3.529 2.329 Back Focal 38.685 75.562 97.163

Surfaces of the lens pieces as identified with reference numerals 6, 24,28 are aspherical in shape. A formula representing aspherical surfacesis given as follows:

$\begin{matrix}{x = {\frac{H^{2}/r}{1 + \sqrt{1 - {A\left( {H/r} \right)}^{2}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}}}} & (10)\end{matrix}$where x is the optical axis, H is a height orthogonal to the opticalaxis, r is a radius of curvature, A is a conical coefficient, and An isthe number of the aspherical surfaces of the n-th degree as expressed bya varied exponent n.

Astigmatism coefficients regarding the surfaces of the lens pieces aregiven as follows:

R6

A=1.0

A4=7.56725E-06

A6=−7.65747E-09

A8=−2.26456E-11

A10=1.23747E-13

R24

A=1.0

A4=7.89296E-06

A6=9.60742E-09

A8=3.69345E-11

A10=−7.34306E-13

R28

A=1.0

A4=−3.19107E-05

A6=−5.55382E-09

A8=−3.27936E-11

A10=3.69412E-13

Focal lengths of the lens groups are given as follows:

1st Lens Group LG1 Focal Length f1 = 108.563 2nd Lens Group LG2 FocalLength f2 = −13.813 3rd Lens Group LG3 Focal Length f3 = 45.230 4th LensGroup LG4 Focal Length f4 = 48.815 Leading Set Focal Length f3a = 26.822of the 3rd Lens Group LG3 Trailing Set Focal Length f3b = −40.500 of the3rd Lens Group LG3

Values of the primary terms in the formulae set forth above in thecontext of the preferred embodiments according to the present inventionare given as follows:f1/ft=0.4030  (11)|f2|/ft=0.052  (12)f3/ft=0.1737  (13)

Aberrations developed in each embodiment of the high variable power zoomlens according to the present invention are depicted in the accompanyingdrawings. In graphs illustrating axial spherical aberration and comaticaberration, ‘d’ denotes the d-line (587.56 nm), and ‘g’ designates theg-line (435.83 nm). In the graphs illustrating astigmatism, a height ofthe image is represented as Y=f14.5, the solid line shows aberration ofsagittal image distortion while the broken line shows aberration ofmeridian image distortion. In the graphs illustrating aberration ofdistortion, the height of the image is given by Y=14.5.

1. In a variable power zoom lens of multi groups of lens pieces, namely,the 1st lens group of positive refractivity, the 2nd lens group ofnegative refractivity, the 3rd lens group of positive refractivity, andthe 4th lens group of positive refractivity arranged in this order onthe closer to objects first basis, the power is varied from thewide-angle end to the telephoto end as a result of the 1st and 2nd lensgroups being separated more, the 2nd and 3rd lens groups coming closerto each other, and the 3rd and 4th lens groups also coming closer toeach other, and the 3rd lens group has a leading set of lens piecescloser to the object side having a positive refractivity as a whole anda trailing set of lens pieces having a negative refractivity as a whole,and the trailing set alone are moved in position orthogonal to theoptical axis to compensate for defocus in the imaging plane caused by atremor of the user's hand(s) while the 2nd lens group is displacedcloser to objects for the focusing of which requirements are to satisfythe following formula:0.14<|f3r/ft|<0.18  (9)  where f3r is a focal length of the trailing setof the 3rd lens group, and ft is the focal length of the entire opticsof the zoom lens at the telephoto end, and wherein the leading set ofthe 3rd lens group has three or more positive lens pieces at least oneof which is a composite lens joined with a negative lens piece, andanother negative lens piece(s).
 2. The variable power zoom lensaccording to claim 1, wherein the leading set of the 3rd lens group hasat least a positive lens piece that is 80 or even higher in Abbe number.3. The variable power zoom lens according to claim 1, wherein thetrailing set of the 3rd lens group includes a composite lens comprisingan anterior negative lens piece and a posterior positive lens piecejoined to the same, the negative lens piece having its opposite majorsurfaces as concaved, the composite lens comprising an asphericalsurface and the positive lens piece has its surface closer to objects asconvexed.
 4. The variable power zoom lens according to claim 1, whereinthe 1st lens group includes three of the lens pieces, namely, acomposite lens of negative and positive lens pieces joined together, andanother stand-alone positive lens piece, and at least one of both thepositive lens pieces is 80 or even higher in Abbe number.
 5. Thevariable power zoom lens according to claim 1, wherein the 1st lensgroup includes three of the lens pieces, namely, a composite lens ofnegative and positive lens pieces joined together, and anotherstand-alone positive lens piece, and at least one of both the positivelens pieces is 1.55 or even higher in refractive index.